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Inaccurate (?) Temps Leading To Fast Idle


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Hey guys - I am getting a fast idle condition occasionally. What I have finally figured out is that when it happens, the temp gauge in the truck is sitting on 160, when I know there is no way in hell it could be that cool. The truck is stock, and to the best of my knowledge has the stock t-stat.



Example - Drove to work today in 90 degree weather. 20 miles or so of 55-75 on the freeway. When I exit the freeway and pull up to a stoplight, I notice that I have the fast idle, around 1k rpms while sitting @ a stoplight with my foot on the brake, and the temp gauge is ALL THE WAY to the left, sitting on 160. Make a 5 min stop, get back in the truck, fire it up, and temp gauge goes immediately to ~200, and the idle is fine.


So it seems to me that the bad temp readings are causing the computer to run the truck richer than it should be, and it runs like crap because the engine is actually 50* warmer than the computer thinks it is.


This leads me to assume there is a temp sending unit that feeds the gauge and the computer or the computer which feeds the gauge.


Am I close here? Is this more likely a sending unit type problem, or could it be the T-stat sticking open or something like that?

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